Added utility scripts and data structures

[fourthedesign]

Added Assets/Scripts/Utilities folder with:

• Extensions.cs : a script which includes many extension methods for unity classes, components, and other structures.
• Attributes
  • ConditionalProperty/ : Use this attribute to make a property only show in inspector if another boolean variable in the inspector is enabled
  • ReadonlyInspector/ : Add this attribute to display a property in inspector, but not allow it to be edited.
  • EditorScripts/ (Moved to Utilities/ on 772c41b): Two scripts, one that ads the right click option to set the anchors of a UI element to its corners, and one that can simulate a click event on a button, during runtime, by right-clicking the button component and clicking on the option.

Added Assets/Scripts/DataStructures folder with:

• SingleUnityLayer/: Use this structure to defined a property that allows the user to select only a single layer in the editor